The position of a mobile station (device), such as, for example, a cellular telephone, may be estimated based on information gathered from various systems. One such system may include the Global Positioning System (GPS), which is one example of a satellite positioning system (SPS). SPS systems, such as GPS, may include a number of space vehicles (SV) orbiting the earth. Another example of a system that may provide a basis for estimating the position of a mobile station is a cellular communication system including a number of aerial and/or terrestrial base stations to support communications for a number of mobile stations.
A position estimate, which may also be referred to as a position “fix”, for a mobile station may be obtained based at least in part on distances or ranges from the mobile station to one or more transmitters, and also based at least in part on the locations of the one or more transmitters. Such transmitters may comprise SVs in the case of an SPS and/or terrestrial base stations in the case of a cellular communications system, for example. Ranges to the transmitters may be estimated based on signals transmitted by the transmitters and received at the mobile station. The location of the transmitters may be ascertained, in at least some cases, based on the identities of the transmitters, and the identities of the transmitters may be ascertained from signals received from the transmitters.
In a Code Division Multiple Access (CDMA) digital cellular network, the position location capability can be provided by Advanced Forward Link Trilateration (AFLT). In Wideband Code Division Multiple Access (WCDMA) and Long Term Evolution (LTE) networks, the position location capability is provided by Observed Time Difference Of Arrival (OTDOA). These techniques compute the location of the mobile station (MS) from the mobile station's measured time of arrival of radio signals from the base stations. A more advanced technique is hybrid position location, where the mobile station employs a Global Positioning System (GPS) receiver and the position is computed based on both AFLT (or OTDOA) and GPS measurements.
LTE OTDOA positioning technology uses Positioning Reference Signals (PRS) to measure Time Of Arrival (TOA) from each neighboring cell in order to calculate an OTDOA position fix. In order to be able to measure the PRS signals from the serving cell and neighbor cells, user equipment (UE), or a mobile device, send an assistance data request to an OTDOA system server. The server will then send a suite of cells' information (e.g., cell configuration and timing info) to the UE. The server can also “push” the cells' information to the mobile device without the mobile device requesting the information. The information provided to the mobile device, by way of the generated assistance data, helps the mobile device search for the PRS (Positioning Reference Signals). For example, the server can send timing information, such as a search window of the cell. The provided search window relates to an estimated TOA of the PRS within that cell. However, some conventional servers for such positioning systems include fairly rudimentary logic for determining the search window to be included in the OTDOA assistance data. For example, some servers presume a physical location of the mobile device with respect to the cell (e.g., center or border of the serving cell) which may lead to an unnecessarily large estimated search window as well as an inaccurate search window center for at least some of the OTDOA measurements.
The OTDOA positioning component of the mobile device typically shares the same hardware correlator resource with the cellular component, and thus, the number of correlators available to the OTDOA positioning component may be limited. Therefore, searching for PRSs based on unnecessarily large search windows and the inaccurate search window center may extend the time that it takes the mobile device to get a position fix and/or may limit the accuracy of the fix by limiting the number of PRS signals used because of time/resource constraints within the mobile device, itself.
Furthermore, some communication systems may allow cells to express support of different band class numbers to allow mobile devices supporting different frequency channel numbers in different band classes to use the same physical cell. However, some conventional OTDOA servers may only provide OTDOA assistance data on a single channel number, regardless of the band or the channel number supported by the mobile device.